Automatic switching apparatus



March 2, 1943. c. E. LoMAx AUTOMATIC SWITCHING APPARATUS Filed Jan. ll, 1941' 1||||o MN: EL T Patented Mar. 2, 1943 UNITED STATES PATENT OFFICE AUTOMATIC SVVITCHING APPARATUS Application January 11, 1941, Serial No. 374,073

15 Claims.

The present invention relates to automatic switching systems and, more particularly, to improvements in the impulse controlled equipment of the switchgear conventionally used in automatic systems of telephonie communication.

It is an object of the present invention to provide for use in a system of the character described a plural digit impulse-controlled automatic switch which is entirely accurate and reliable in its response to impulses transmitted thereto over lines having inferior impulsing characteristics.

It is a further object of the invention to provide an automatic switch of the character described which includes a line or pulsing relay which is so arranged relative to the other relays of the switch that it is subjected to an electromagnetic priming action during each of the digits transmitted to the switch.

It is another object of the invention to provide an automatic switch of the character described which is so arranged that the operation of the line relay is iniiuenced and improved by the electromagnetic coupling provided between this relay and the change-over or digit transfer relay of the switching during each digit transmitted to the switch.

It is still another object of the invention to provide an automatic switch of the character described which is so arranged that the operation of the line relay is influenced and improved by the electromagnetic coupling provided between this relay, the hold or release relay and the change-over or digit transfer relay, during each series of impulses transmitted to the switch.

The invention is illustrated in its embodiment in a connector switch forming a part of a small automatic telephone system. More specically, the connector switch is of the two-motion, twodigit type utilizing vertical and rotary magnets for effecting the primary and secondary movements of the movable switch wipers. The first digit transmitted to the switch is utilized for line group selection and the second digit is utilized for the selection of a particular line ina.

selected group. The impulse controlled equipment of the switch includes the usual line relay, a slow-acting hold or release relay, and a slowto-release change-over or digit transfer relay of the series type, which is utilized to effect a transfer of the pulsing circuit local to the switch from the vertical or group select magnet to the rotary or units select magnet of the switch. In accordance with the present invention provisions are made for energizing this change-over relay during each of the two digits transmitted to the switch in setting up a connection, and this relay, the line relay and the hold relay are so positioned and poled with respect to each other that the operation of the line relay accurately to follow the impulses transmitted thereto, is substantially improved. More speciiically, the magnetic circuit of the line relay is disposed within the magnetic iields resulting from energization of the release and change-over relays, and the magnetic circuits of these three relays are so related that the flux linking with the magnetic circuit of the line relay and occasioned by the energization of the change-over relay, assists or enhances the energization of the line relay, while the ux linking the magnetic circuit of the line relay and resulting from energization of the release relay, assists in the deenergzation of the line relay.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof will best be understood by reference to the speciiication taken in connection with the accompanying drawing in which Fig. 1 illustrates the invention as embodied in a connector switch forming a part of a small automatic telephone system, and Fig. 2 illustrates the physical arrangement of the line, release and change-over relays embodied in the connector switch shown in Fig. 1.

Referring now more particularly to Fig. 1 in the drawing, the system there illustrated has an ultimate capacity of lines and may be utilized to serve a small community which forms a part of a larger central exchange area, suitable ring-down trunks being provided for routing Connections from the exchange equipment of the community exchange to a central office, not shown, of the manual type. Brieiiy described, the illustrated system comprises a plurality of subscriber lines lil, Il, etc. which individually terminate in the community exchange in line circuits Illa, Ha, etc. The two lines le and Il extend to the substations A and B, respectively, each of which conventionally includes substation equipment of the common battery type. More specifically, each substation comprises the usual transmitter and receiver, a hybrid system, a dialcontrolled impulsing device, a hook switch and a bell or ringer.

For the purpose of setting up connections between the lines l0, il, etc., the exchange is equipped with a plurality of iinder-connector links, one of which is illustrated as including the nder I2 and the connector I5, which are automatically allotted for use by a link distributor I3. Although the distributor I3 may be of any desired commercial form, it is preferably of the preselective rotary type, such that an idle link is selected for use immediately a previously selected link is seized over a calling line. The line finders of the system may similarly be of any desired type, although preferably are of the Well-known Strowger type utilizing two-motion Sirowger switches for line selecting purposes.

rIhe connectors of the exchange are also of the Strowger type. These switches areA identical in construction and arrangement and, accordingly, the physical structure and circuit wiring thereof will be understood from a consideration of theV connector I5. Briefly described, this connector comprises a Strowger switching mechanism which includes a stationary contact eld divided into levels, a set of movable Wipers ||2 to II5, inclusive, the usuallvertical, rotary and release magnets |83, |84 and |85, respectively, and vertical olf-normal springs |81 and |88. The enumerated magnets are arranged to be controlled b-y a set of relays which includes a battery reversing relay Rl, a line or pulsing` relay RIIll, a slow-torelease hold or release relay RI20, a slow-acting ring cut-off relay RI30, a busy` test relay Rl4j, a series change-over or digit transfer relay RI50, a transfer relayV RIGII, a sloW-to-release control relay RII0, a trunk-hunting relay RI80, and a sloW-to-cperate line switching relay RI 90. These relays are interconnected to control the vertical, rotary and release magnets of the switch, and

also the line switching required incident to the completion of a connection, by circuits which are described with particularity hereinafter.

In considering the operation of the system it may be assumed that a call intended for the substation B is initiated at the substation A. To initiate the call the calling party removes the telephone instrument provided at the substation A from its supporting hook or cradle, in the usual manner, whereby the associated hook or cradle switch is operated to complete a calling circuit which includes the conductors of the line I and extends to the line circuit Illa. When this circuit is completed the line relay convention-ally embodied in the line circuit lila operates to mark the calling line I0 in the bank contacts of the nders provided in the exchange and to impress ground or start potential upon the distributor start lead I4. Assuming that the distributor I3 has previously operated to select the illustrated iinder-connector link for use, the application of :ground potential to the distributor start lead I4 results in the operation of the finder I2 to seize the calling line I6 through the line circuit I0a.1

More specifically, the relay equipment of the distributor I3, operating rst in conjunction With the vertical magnet of the finder I2, causes the wipers of this finder to move vertically to a posi tion opposite the level of bank contacts in which the conductors cf the line I0 are terminated.

vAfter this level is located a transfer operation the cut-off relay of the line circuit IUa. Incident to these operations the calling loop circuit is extended to the connector I5, the line I0 is marked as busy, and a guard potential is impressed upon the guard lead individual to the nder I2 to mark the illustrated link as busy in the test contacts of the distributor switch forming a part of the distributor I3. When the cut-off relay of the line circuit |0a operates, the distributor start lead I4 is disconnected from ground, and operation of the distributor switch is initiated to select another idle link for the use of the next incoming call. The manner in which all of these operations are effected is well lunderstood in the art and will be readily understood from the above brief explanation.

As indicated above, when the nder I2 operates I -to seize the calling line I0, it extends the calling loop circuit through the contacts |02 and |04 of the battery reversing relay RI 00 to the terminals of the line relay RI III so that the line relay is energized thereover. In operating, the'line relay RIIII closes its contacts to complete an obvious circuit for energizing the release relay R I 20. The relay R|20, upon operating, closes its contacts I2I to complete an obvious path for impressing ground potential upon the release conductor IIB, thereby to complete locking circuits for the operated cut-through relayV of the iinder I2 and the operater cut-olf relay of the line cir.- cuit I0a. At its contacts |22, the relay RI20 prepares a circuit for energizing the change-over relay R|50 in series with the vertical magnet |83 during the rst series of impulses transmitted to the connector I5. At its contacts |23, the relay R|20 opens a point in the circuit for energizing the release magnet |85. At its contacts |24, the relay R|20 prepares certain operating and locking circuits referred to more specifically hereinafter. Following the operation of the two relays RI I0 and RI20 the connector I5 is conditioned to respond to the impulses of the first digit of the directory number designating the desired substation B. During the impulses of this digit, as transmitted through operation of the calling device provided at the'substation A, the line relay RI I0 alternately operates and restores one or more times, depending upon the numerical value of the digit. Assuming that the directory number designating the called substation B is 44, the line relay RI I0 restores and reoperates four times during each of the first and second digits. Each time the relay RI I0 restores, it opens its contacts I I I to interrupt the operating circuit for the release relay RI20. When the line relay RLIIJ rst restores at the beginning of the open-circuit period of the iirst impulse the above-mentioned circuit is completed for energizing the relay RI50 in series with the vertical magnet |83, this-circuit extending from ground by way of the contacts III', |22 and |45, the winding of RI5|'|, the contacts IBI and the winding of the magnetl |83 to battery. When energized over this circuit the relay RI 50 operates and closes its contacts |52 to complete an obvious path in shunt with the break contacts |45 controlled by the busy test relay RI40. At its contacts |5I, the relay R|50 opens a point in the operating circuit for the trunkhunting relay RI80. At its contacts |53, the relay R|50 prepares one of the operating circuits for the slow-to-release control relay RI 10. At its contacts |54, the relay RI50 opens a point in the other operating circuit for the relay RIIU. The vertical magnet |83, upon operating in response to the completion of the circuit traced above, co-

,operates with its associated `ratchet and pawl mechanism to elevate the wipers I|2 to v| I5, inelusive, one step so that these Wipers are positioned opposite the first level of bank contacts in the associated contact field. In response to the vertical movement of the wipers, the vertical offnormal springs |81 are moved into engagement to lprepare the operating circuit for the release mag- -net |85 and the vertical off-normal springs |88 are closed to prepare the operating circuit for the transfer relay RI 60. It will be understood that at the end of the open-circuit period of the first impulse when the line relay RIIU reoperates the vertical magnet |83 is deenergized. It will also be understood that three additional current pulses are transmitted to this magnet through the winding of the change-over relay R|5|l by the line relay RI I during the rst digit. Each time the vertical magnet |83 is energized it operates to lift the associated wipers I I2 to II5, inclusive, an additional step. Accordingly, these wipers are left standing opposite the fourth level of bank contacts in which the conductors of the called line are terminated at the end of the first digit. Due to the slow-to-release characteristics thereof, the release relay R|2 and the change-over relay RIE!! remain operated during impulsing.

Shortly following the end of the rst digit and during the inter-digit pause between the first and second digits the change-over relay R|5 restores to complete the prepared operating circuit for the transfer relay R455, this circuit extending from ground by way of the off-normal springs |88, the contacts |55 the winding of RISO to battery. When thus energized the relay RI'GII operates and locks to ground over a path including the contacts |54 and |24. At its contacts |63, the relay Rieu prepares the operating circuits for the relay Rll. At its contacts IGI, the relay Rlil opens the above-traced circuit over which current pulses were delivered to the vertical magnet during the dialing of the first digit. At its contacts |52, the relay RIM prepares a circuit for energizing the rotary magnet |84 in series with the change-over relay VR|5Il during the dialing of the second digit. This circuit is completed at the beginning of the open-circuit period of the rst impulse of the second digit and extends from ground by way of the contacts III', |22 and |45, the winding of RI5Q, the contacts |62 and |95 and the winding of the magnet |84 to battery. In reoperating, the relay R|50 closes its contacts |53 to complete the prepared operating circuit for the relay RH!! and opens its contacts |55 to interrupt the operating circuit for the transfer relay RIGIJ. At its contacts I5|, the relay 'RI55 opens a point in the operating circuit for the trunk-hunting relay RISQ. The rotary magnet |84, in operating, rotates the wipers ||2 to IIE, inclusive, into engagement with the contacts forming the irst contact set in the selected fourth level. At its contacts |85, the magnet |84 opens another point in the operating circuit for the trunk-hunting relay RI 8B. It will be understood that the rotary magnet |84 is Adeenergized when the line relay RI I5 reoperates to terminate the open-circuit period of the first impulse in the second digit. It will also be understood that during each succeeding impulse of this digit a current pulse is delivered to the rotary magnet |84 through the winding of the relay R|50, so that at the end of the second digit vthe wipers I I2 to I I5, inclusive, are left standing in `engagement with the contacts terminating the conductors of the line During this rotary movement of the switch wipers, the busy test relay RI40 is energized each time the test wiper I5 engages a contact terminating the private conductor of a busy line. Thus the relay RFID, upon operating at the beginning of ,the second digit, closes its contacts |14 to connect the busy test relay RMI) to the test wiper ||5, whereby this relay is energized each time the test Wiper engages a test contact marked with ground potential indicating that the associated line is busy. In operating, the relay RI10 ralso opens its contacts I1 to prevent busy tone current from being projected over the calling loop circuit during the rotary movement of the switch wipers, and closes its contacts |12 to prepare the operating circuit for the trunk-hunting relay RISE). At its contacts |15, the relay R|10 opens a point in the locking circuit for the busy test relay RIM). At its contacts |13, the relay R|15 opens a point in the operating circuit for the idle test or switchthrough relay RIQD.

As indicated above, immediately the called line II is selected it is tested to determine the idle or busy condition thereof. In the event the line is busy the private conductor thereof is marked with ground potential in lthe line circuit ||a so that the busy test relay R|45 is energized over the above-mentioned test circuit. This circuit extends by way of the grounded test Contact individual to the line Il, the test wiper II5, the contacts |14 and |94, and the winding of RIM) to battery. In operating, the relay RMI) closes its contacts |43 to prepare a locking circuit for itself; opens its contacts |45 to interrupt the initially completed pulsing circuit extending through the Winding of the change-over relay RI5D to the rotary magnet |84; and closes its contacts |42 further to prepare the operating circuit for the trunk-hunting relay R555. At its contacts |4I, the relay RMB prepares the abovementioned circuit for transmitting busy tone current over the calling end of the connection. At its contacts |44, the relay Ri|4 opens a point in the operating circuit for the switch-through relay RISO.

Shortly following the selection of the called line I in the manner pointed out above, the two relays R|55 and RII!) sequentially restore, in the order named and in an obvious manner. 'In releasing, the relay R|5|l closes its contacts |51i further to prepare the operating circuit for the trunk-hunting relay RISI] and opens its contacts |52 to interrupt the pulsing circuits to the Vertical and rotary magnets, thus preventing any further response on the part of the connector to additional impulses transmitted thereto. The relay RI1B, upon restoring, closes its contacts |15 to complete the above-mentioned locking circuit for the busy test relay RIM), this circuit extending from ground by way of the contacts |2I, |43, |15 and |94, and the winding of RIM to battery. After this circuit is completed the relay RIM opens its contacts |14 to interrupt the operating circuit for the busy test relay. At its contacts I1I, the relay RVS completes the above-mentioned circuit for transmitting a busy tone signal over the calling end of the connection, this circuit extending Afrom the ungrounded terminal of the busy tone current source, not shown, by way of the conductor |45, the contacts |1I, the condenser |65, the contacts i4! andthe condenser |59 to one side of the loop circuit extending to the calling substation. From this point the current is transmitted through the receiver provided at the substation A and over the opposite side of the line I to the opposite terminal of the busy tone signal source. 'The reproduction of this current by the receiver provided at the calling substation serves to inform the calling party that the desired connection .cannot be obtained. Following the operations just described no further operation of the apparatus included in the switch train occurs until the call is abandoned at the calling substation. The manner in which the link is released when the calling party restores the telephone instrument at the calling substation to its supporting hook or cradle will be clearly apparent from the following explanation.

In the event the called line II is idle at the time it is selected, the test or private conductor thereof is marked with negative battery potential so that the busy test relay Rl 40 is short-circuited over the above-traced test circuit and fails to operate. Accordingly, when the relays R|50 and R|`|0 restore shortly followingfthe end of. the second digit the operating circuitl for the slow-tooperate switch-through relay is completed, this circuit extending from ground `by way of the contacts |2| and |44, the upper winding of RI190, the contacts |13, the test wiper ||5 and engaged test contact, the private conductor of the line |I and the winding of the cut-off relay embodied in the line circuit I la to battery. When thus energized the relay R|90 operates and Closes its contacts |96 to complete a holding circuit for itself, this holding circuit extending rom ground yby way of the contacts |24 and |96, and the lower Winding of R|90 to battery. At its contacts |93, the relay RI 90 completes a circuit for impressing ground potential directly upon the test wiper I I5, thereby to increase the energization of the cut- 01T relay embodied in the line circuit IIa and to mark the line II as busy in the bank contacts of the other connector switches. At its contacts |94, the relay RI90 opens another point in the operating and locking circuits for the busy test relay RI40. At its contacts |95, the relay RI90 opens another point in the operating circuit for the rotary magnet |84. At its contacts |9| and |92, the relay Rl 90 completes a circuit over which ringing current is transmitted to energize the ringer provided at the called substation B. The cut-off relay of the line circuit lia, in operating, disconnects the windings of its associated line relay frorn the talking conductors of the line |I to clear this line of the shunt impedance represented by the line relay windings.

The circuit traversed by the ringing current :following operation of the switch-through relay 1R|90 may be traced as extending from the run- ;grounded terminal of the ringing current genera- '.tor, not shown, by way of the contacts |33 and 192, the wiper ||3, the positive side of the line il, the bridged ringer and condenser vconnected across the conductors of the line I at the substation B, the negative side of the line I I, the wiper ||2, the contacts I9I and |3I, the upper winding of RI 30 and the exchange battery to the grounded terminal of the ringing current generator. A portion of the current traversing this circuit is by induction repeated to the lower winding of the ring cut-off relay RI 30 and is transmitted,

over the calling end of the connection to signal the calling subscriber that the called substation is being rung. The ringer provided at the substation B similarly responds to the ringing current by operating to signal the called subscriber that a call iis presenten the line lII which should -beanswered.' Y '1, I f The desired talking circuitl between the `calling and .called substations is completed when thecall is answered at the called substation. More specifically, whenthe' telephone instrument at the called substation B is removed from its supporting hook or cradle, a direct current circuitis completed for energizing the ring cut-off relayjRI3lJ.` This circuit extends from ground by way of the ringing current generator, the contacts |33 and |92, the wiper I|3, the positive line side of the line I I, the direct current bridge vacross the conductors of this line at the called substation, the negative side of the line II, thew'iper ,II2, the contacts I9I and I3I and the upperwinding of RI30 vto battery. When thus energized, the relayR| 30 closes its preliminary make contacts |35 to complete a locking circuit for itself which extends from ground by way of the .contacts |24 and |35, and the lower winding of RI30 to battery. After this locking circuit is completed the relay-RI30 opens its contacts |3| 4and |33 to interrupt the circuit traversed by the ringing current and two points in its operating circuit as traced above. At its contacts |32 and |34, the relay RI 30 completes the desired talking circuit between the calling and called substations, and in so doing closes a circuit for energizing the -battery reversing relay RI00. The latter circuit may be traced as extending from ground by way of the contacts |24 and |35, the lower winding of'RIil, the contacts |34 `and |92, the wiper H3, the Apositive side of the line II, the direct current bridge across the conductors of this line at the called substation, the negative side of the line, the wiper II2, the contacts I'9I and |32, and the upper winding of RI00 to battery. It will be understood that current for energizing the transmitter provided at the called substation is delivered over this circuit. Similarly, current for energizing the transmitter provided at the calling substation is transmitted through the windings of the line relay RIIO. When energized over the circuit just traced the relay RI00 operates and closes its contacts |06 to complete obvious multiple locking circuits for itself and for the relays RI30 and R|90. At its contacts |05, the relay RI00 opens another point in the operating circuit for therelease magnet |85. At its contacts I 0| to |04, inclusive, the relay RI00 reverses the direction of current flow over the calling loop circuit, this current reversal being without effect in handling Ia call of the character under consideration. It is noted, however, that this current reversal may be utilized for supervisory purposes in handling calls routed to the link from an operators yposition in the distant central office. Following the operation of the battery reversing relay RI 00 no further operation of the apparatus occurs until the connection is released.

The connector I5 is of the last-party-release type, i. e., it is only restored to Vnormal after a connection routed therethrough has been released at both the calling and called ends thereof. Thus it will be apparent that if theY called subscriber restores the instrument provided at the called substation to its supporting hook or cradle the only relay operation resulting therefrom is the deenergization and release of the battery reversing relay RI00. In restoring, this relay opens its contacts |06 to interrupt the multiple locking circuits for the relays RI30 and RISO, closes its contacts |05 to -reprepare the operating circuit for the release magnet |85, and reverses the direction` of current 'ow over the calling loop circuit. If the connection is subsequently released at the calling end thereof the line and realese relays RI IIJ and R|2Il are caused sequentially to restore, in an obvious manner. The relay RIZII, in restoring, opens its contacts |24 to interrupt the locking circuits for the relays R|39 and RISG. At its contacts |2I, the relay R|2Il opens one of the paths over which ground potential is impressed upon the release conductor IIS. It will be noted, however, that ground potential is maintained upon this conductor over a path which includes the contacts |64 and |55 and the off-normal springs |88. At the contacts |2I, the locking circuit for the transfer relay RIBI) is also interrupted but this relay remains in its operated position due to the continued energization thereof over its operating circuit as traced above. The relay RI90, upon restoring, opens its contacts |93 to disconnect the private conductor of the line I from ground and thus cause the deenergization and release of the cut-off relay embodied in the line circuit Illa. When this cut-off relay restores the line circuit Ia is fully released and the line is marked as idle in the contacts of the connector switches to which it is accessible.

In restoring, the release relay R| completes the prepared operating circuit for the release magnet I 85, this circuit extending from ground by way of the contacts III', |23 and |05, the OIT-normal springs |8'I and the winding of the magnet |35 to battery. When thus energized the magnet |85 attracts the holding pawl of the Strowger switching mechanism, whereby the wipers ||2 to II5, inclusive, are restored to rotary and vertical normal in the usual manner. When these wipers are returned to normal the olf-normal springs |81 and |88 are respectively disengaged to cause the deenergization and release of the magnet |35 and the relay RIIIl, respectively. Following the operations just described the connector I5 is fully restored. to normal. When the oil-normal springs |88 are opened, the release conductor |6is disconnected from ground to cause the release of the finder I2 and the line circuit Illa in a manner well understood in the art. Incident to the release of the finder I2 the link busying potential is removed from the guard conductor individual to the link illustrated, whereby this link is rendered available for selection by the distributor I3. Incident to the release of the line circuit Illa, and more specifically the release of the cut-01T relay embodied therein, guarding ground potential is removed from` the private conductor of the line II) and negative battery potential is impressed upon this conductor'to mark the line I0 as idle. From the above explanation it will be apparent that in the event the called line is busy at the time it is selected the release of the switch train proceeds in substantially the manner described above. In this regard it will be apparent that the busy test relay RI40 is deenergized and restores when the release conductor IIB is disconnected from ground.

In the event the connection is cleared out at the calling end thereof before it is released at the called substation the line relay RIIU and the hold relay RIZl are deenergized and restored, in the order named. In such case the battery reversing relay RIIIIJ is operated at the time the relay RIZI) restores. Accordingly, the two relays RIS!! and RIS!! are prevented from releasing and the circuit for energizing the release magnet is held open at the contacts |55. Moreover, ground potential is maintained on the release conductor ||6 over a path lincluding the off-normal springs |83 and the'contacts I 55 and |54, thus preventing the release of the nder I2 and the line circuit Ilia. When the connection is subsequently released at the called substation, the relay RID!! restores to open the locking circuits for the relays R|3II and RIBI) and to complete the prepared operating circuit for the release magnet |85. From this point on the release of the connection proceeds in the manner explained above.

In the event the above described call originating at the calling substation A and routed to the connector I5 is of the character requiring the assistance of a central ofce operator for completion, the calling subscriber dials the central office directory number which comprises two digits. The irst of these digits designates the contact level in which the ring-down trunks extending to the central office are terminated, and the second digit designates the iirst trunk of the group. Automatic trunk hunting facilities are provided in the connector I5 so that if the first trunk of the group is busy the remaining trunks are tested in succession until an idle trunk is found or until all of the trunks have been tested. To this end, the private and extra control contacts individual to each central oiiice trunk, with the exception of the contacts individual to the last trunk of the group, are strapped together in the manner indicated by the strap |91 extending between the private contact |98 and the extra control contact ISQ. With this wiring arrangement, if' the Wipers ||2 to II5, inclusive, are operated in the manner explained above to engage the contacts terminating the i-lrst trunk of the group at a time when this trunk is busy, a circuit is prepared for energizing the trunk-'hunting relay RI 8|) and the previously traced circuit is completed for energizing the busy test relay RIM. Shortly following the selection of this trunk the relay RI 5I) restores and closes its contacts |5| to complete the operating circuit for the trunkhunting relay RISE?, This circuit extends by way of the grounded extra control wiper II4, the contacts |72, |5I, |42 and |86, and the winding of Rll to battery. It will be noted that if the private and extra control contacts individual to the first trunk of the group are marked with negative battery potential indicating that the trunk is idle, the relay R|4D and the relay RI8 are short-circuited and fail to operate during the test period. Accordingly, the call is permitted to proceed over the first trunk to the distant exchange in the manner explained above withreference to the call routed to the substation B.

Assuming that the rst trunk of the group is busy, the relay RIB is energized and operates to complete a locking circuit for itself which extends from ground by way of the contacts I2I, ISI and |86 and the winding of RI80 tobattery. At its contacts |82, the relay RIBiB completes an alternative circuit for energizing the rotary magnet |84 in parallel with the slow-torelease control relay RI'IIJ. This circuit extends from ground by way of the contacts |24 to the contacts |52 where it divides, one branch extending through the contacts |95 and the winding of the magnet |84 to battery and the other branch extending by way of the contacts |62, |54 and |53 and the winding of RI'I to battery. When thus energized the rotary magnet |84 operates to step the wipers IIE to II5, inclusive, into engagement with the contacts terminating the conductors of the second trunk in the selected group. At its contacts |86, the magnet |84 opens the operating and locking circuits for the trunk-hunting relay RI 80.` The relay R|8IJ now restores and opens its contacts |82 to deenergize the relay RI`| and theV rotary magnet |84. At its contacts I8|, the relay RI80 further interrupts its own locking circuit. The rotary magnet 84, upon restoring, recompletes the test circuit over which the trunk-hunting relay RIB!! is energized. In this regard it will be noted that if the second trunk of the group is also busy, ground potential is retained upon the private and extra control Wipers |I and II4, thus preventing the release of the busy test relay R|40 and causing the reenergization of the trunk-hunting relay RIM when the rotary magnet |84 releases. The interrelated operation of the relay RIBU and the rotary magnet |84 continues until an idle trunk in the group is found or until all of the trunks have been tested and found to be in a busy condition. Due to the slow-to-release characteristic thereof, the relay RI'IIJ remains operated during the trunk hunting operation just described.

Assuming that ani all-busy condition of the trunks exists, the wipers I 2 to II5, inclusive, are rotated to engage the contacts terminating the last trunk of the group. In the terminaion of this trunk the strap between the private and extra control contacts individual thereto is omitted. Accordingly, no further circuit is available for energizing the trunk-hunting relay RIB!! but a circuit is available for maintaining the energization of the busy test relay RI40. In this case the relay RIBU, upon restoring, deenergizes the relay RI10, permitting the latter relay to restore after an interval. In releasing the relay RI`|0 completes the locking circuit for the busy test relay RI4IJ and closes the circuit for transmitting a busy tone signal to the calling subscriber. The manner in which the connection is released under the control of the calling subscriber following the receipt of the busy signal is exactly the same as described above.

Assuming that one of the trunks in the selectedgroup is idle, the trunk-hunting operation on the part of the connector I5 is arrested when this trunk is selected. More specifically, when av trunk having its private and extra control contacts marked with negative battery potential Iis selected by the connector I5, the busy tes. re-

lay RI40 is deenergized and restores and no further circuit is available for energizing the trunk-hunting relay RI80. Accordingly, the relay RI'IO restores after an interval to complete the prepared operating circuit for the switchthrough relay RISO. From this point'on the `manner in which the call proceeds to the cen- Vsubstantially as shown in Fig. 2 of the drawing.

Although each relay has a separate heelpiece, the magnetic circuits thereof vare in such close proximity to each other that a certain amount of leakage flux from the core or magnetic circuit of one relay links the core or magnetic circuit of each adjacent relay. Since the line relay RI 0 is in the center, disposed between the other two relays, it is in a position to influence and to be influenced to the greatest eXtent by the leakage ux produced by energizaton of each of the other two relays. This influence is greatly enhanced if the line relay RI l0 is provided With a brass heelpiece which substantially increases the leakage iiux. The three enumerated relays are Wound in such direction that if the armature end of the line relay RI I0 is a north magnetic pole, for example, the armature end of therelease relay RIZU will also be a ncrth polewhile the armature end of the change-over relay RI50 will be asouth pole, as indicated in Fig. 2 of the drawing. A Y

Considering the operation of the switch in order to explain how the operation of the line relay RIIU is improved, it will be noted that when the line'relay is energized it closes a circuit for the release relay RI20 and theleakage ilux produced by the energization of the latter relay will oppose the iiux traversing the core or magnetic circuit of the line relay. Accordingly, when the circuit of the line relay is broken it will Ybe deenergized more quickly than it would in the absence of the leakage flux linking therewith. On the other hand, when the circuit of the line relay RII 0 is again closed afterthe rst interruption, the energization of the release relay RIZIJ is at a minimum but the change-over relay RI50 is fully energized and the polarity of the latter relay is such-v that the leakage ilux produced thereby and linking with the magnetic circuit ofthe line relay assists in the magnetization of the magnetic circuit of the line relay. Thus an electromagnetic priming action of the line relay RI I0 occurs at the end of the open-l circuit-period of each impulse transmitted to the switch. It Ywill be apparent that this prim'- ing action ofthe change-over relay R|50 is obtained during each of the two digits transmitted to the connector I5 in setting up a connection. Thus the arrangement of the circuit Wiring Yis such that the relay R|50 is energized bothduring the vertical and rotary movement of the connector switch Wip-ers. Accordingly, the advantages achieved by arranging the three relays RIII'I, R|2 and R|5 in the manner explained above are retained throughout both impulsing periods.

While there has been described what is at present considered to be. the preferred embodiment of thevinvention, it will be understood that various modifications may be made therein, and it is contemplated to cover Ain the appended claims all such modifications asA fall Within the l` true spirit and scope of the invention.A

What is claimed is: 'y

v1. In a telephone system, a two-motion impulse responsive connector switch comprising movable contacts, a pair of operating magnets for respectively imparting the two motions to said movable contacts, a line relay, a changeover relay, said line relay being disposed in the magnetic field of said change-over relay and being so arranged that the leakage flux resulting from energization of said change-over relay assists in the energization of said line relay, circuits interconnecting said magnets, said changeover relay and the contacts of said line relay, and means for controlling said circuits so that said change-over relay is energized in series with one of said magnets during the transmission of one series of impulses to said switch and is energized in series with the other of said magnets during the transmission of a succeeding series of impulses to said switch.

2. In a telephone system, a two-motion impulse responsive connector switch comprising movable contacts, a pair of operating magnets for respectively imparting the two motions to said movable contacts, a line relay, a release relay energized in response to operation of said line relay, a change-over relay, said line relay being disposed in the magnetic iields of said release and change-over relays and the three of said relays being so arranged that the leakage flux resulting from energization of said release relay assists in the deenergization of said line relay and the leakage iiux resulting from energization of said change-over relay assists in the energization of said line relay, circuits interconnecting said magnets, said change-over relay and the contacts of said line relay, and means for controlling said circuits so that said changeover relay is energized in series with one of said magnets during the transmission of one series of impulses to said switch and is energized in series with the other of said magnets during the transmission of a succeeding series of impulses to said switch.

3. In a telephone system, a two-motion impulse responsive connector switch comprising movable contacts, a pair of operating magnets for respectively imparting the two motions to said movable contacts, a line relay, a change-over relay, said line relay being disposed in the magnetic field of said change-over relay and being so arranged that the leakage iiuX resulting from energization of said change-over relay assists in the energization of said line relay, and means comprising said line relay for controlling said change-over relay and said magnets so that said change-over relay is energized concurrently with one of said magnets during the transmission of one series of impulses to said switch and is energized concurrently with the other of said magnets during the transmission of another series of impulses to said switch.

4. In a telephone system, a two-motion impulse responsive connector switch comprising movable contacts, a pair of operating magnets for respectively imparting the two motions to said movable contacts, a line relay, a release relay energized in response to operation of said line relay, a change-over relay, said line relay being disposed in the magnetic elds of said release and changeover relays and the three of said relays being so arranged that the leakage flux resulting from energization of said release relay assists in the deenergization of said line relay and the leakage iiux resulting from energization of said changeover relay assists in the energization of said line relay, and means comprising said line relay for controlling said change-over relay and said magnets so that said change-over relay is energized concurrently with one of said magnets during .the transmission of one series of impulses to said switch and is energized concurrently with the other of said magnets during the transmission of another series of impulses to said switch.

5. In a plural digit automatic switch, a line relay, a second relay, said line relay being so disposed within the magnetic iield i said second relay that the leakage iiux resulting from energization of said second relay aiiects the operation of said line relay, and means for energizing said second relay during at least two digits transmitted to said switch.

6. In a plural digit automatic switch, a line relay, a second relay, said line relay being so disposed within the magnetic eld of said second relay that the leakage iiux resulting from energization of said second relay assists the energization of said line relay, and means for energizing said second relay during each of at least two digits transmitted to said switch.

7. In a plural digit impulse controlled automatic switch, a line relay, a change-over r`elay, said line relay being so disposed within the magnetic field of said change-over relay that the leakage ilux resulting from energization of said change-over relay affects the operation of said line relay, means for energizing said change-over relay during each of at least two series of impulses transmitted to said switch, and pulsing circuits controlled by said change-over relay.

8. In a plural digit impulse controlled automatic switch, a line relay, a change-over relay, said line relay being so disposed within the magnetic field of said change-over relay that the leakage flux resulting from energization of said change-over relay assists the energization of said line relay, means for energizing said change-over relay during each of at least two series of impulses transmitted to said switch, and pulsing circuits controlled by said change-over relay.

9. In a plural digit automatic switch, a line relay, and means electromagnetically coupled to said relay for magnetically priming said relay during each of a plurality of digits transmitted to said switch.

10. In a plural digit automatic switch, a line relay including a magnetic circuit, a second relay including a magnetic circuit electromagnetically coupled to the magnetic circuit of said line relay, and means for energizing said second relay during each of a plurality of digits transmitted to said switch.

11. In a plural digit automatic switch, a line relay including a magnetic circuit, a second slowacting relay including a magnetic circuit electromagnetically coupled to the magneti-c circuit of said line relay and so poled that the fluX linking the magnetic circuit of said line relay when said second relay is energized assists the energization of said line relay, and means including said magnetically coupled to said line relay for magnetically priming said line relay during each of a plurality of digits transmitted to said switch.

13. In a plural digit automatic switch, a line relay including a magnetic circuit, a second relay including a magnetic circuit electromagnetically coupled to the magnetic circuit of said line relay and so poled that the flux linking the magnetic circuit of the line relay when said second relay is energized eiiectively changes the energization of said line relay in one sense, a third relay including a magnetic circuit electromagnetically coupled to the magnetic circuit of said line relay and so poled that the iiux linking the magnetic circuit of the line relay when said third relay is energized effectively changes the energization of said line relay in the opposite sense,` and'means for energizing said second and third relays during each of ,a plurality of`v digits transmitted to said switch.

14. In a plural digit automatic switch, a line relay including a magnetic circuit, a sloW-to-release hold relay energized in response to operation -of said line relay and including a magnetic circuit coupled to the magnetic circuit of said line relay, the magnetic circuit of said hold relay being so poled that the flux lnkin'g'the magnetic circuit of said line relay and resulting from energization of ,said hold relay effectively decreases the energization of said line relay,a slow-to-release changeover relay including a magnetic circuit electromagnetically coupled to the magnetic circuit of said line relay and so poled that the flux linking the magnetic circuit of said line relay and resulting from energization of said change-over relay eiectively increases the'energization of said line relay, and means including said line relay for energizing said change-over relay at the beginning of each of aplurality of digits transmitted to said switch.

l5. In a plural digit impulse controlled automatic switch, a line relay including a magnetic circuit, a slow-to-release hold relay energized in response to operatic-n of said line relay and in'.- cluding a magnetic circuit coupled to the magnetic circuit of said line relay, the magnetic cir'- cuit of said hold relay being so poled that the flux linking the magnetic circuit of said line relay and resulting from energization of said hold relay effectively decreases the energization of said line relay, a slow-to-release change-over relay including a magnetic circuit electromagnetically coupled to the magnetic circuit of said line relay and so poled that the flux linking the magnetic circuit of said line relay and resulting from energization of said change-over relay effectively increases the energization of said line relay, means including said line relay for energizing said change-over relay at the beginning of each of a plurality of digits transmitted to said switch, a pulsing circuit controlled by said line relay and having two branches, and means comprising a transfer relay controlled by said change-over relay for opening one of the two branches of said circuit and for completing the other branch of said circuit during the inter-digit pause between two digits transmitted to said switch.

CLARENCE E. LOMAX. 

